1. Field of the Invention
The present invention relates to a method of making a liquid jet recording head, and in particular, a liquid jet recording head for jetting a recording liquid used in the so-called ink jet recording process to form flying droplets of the recording liquid.
2. Description of the Prior Art
An ink jet recording method (liquid jet recording method) enables high speed recording with negligible noise being generated during recording and also enables recording on a plain paper without requiring fixing or other special treatment. Accordingly, interest in this method has been increasing.
A liquid jet recording method disclosed in Japanese Patent application Laid-Open No. 54-51837 and German application DOLS No. 2843064 has a feature different from a conventional liquid jet recording method in that heat energy is applied to liquid to generate a motive force to jet the liquid droplet.
The method disclosed in the above patent applications is characterized in that liquid acted on by the heat energy creates a change of phase which results in a rapid increase in volume and liquid is jetted from an orifice at an end of a recording head by the change of phase so that a flying liquid droplet is formed and deposited on a record medium to form a record.
Particularly, the liquid jet recording method disclosed in the German application DOLS No. 2843064 is not only effectively applicable to a so-called drop-on demand recording method but also enables implementation of a recording head of a full line type having a high density multi-orifice head. Thus, it can provide a high resolution and high quality image at a high speed.
The recording head used in a device for the above method includes a liquid jet unit having an orifice for jetting liquid and a liquid path communicating with the orifice for forming a heat applying unit which applies heat energy to the liquid to jet a liquid droplet, and an electro-thermal transducer for generating the heat energy.
The electro-thermal transducer includes a pair of electrodes and a heat generating resistance layer connected to the electrodes for defining a heat generating region (heat generating portion) between the electrodes.
When such a liquid spray recording head is used, the electrodes and heat generating portions between the electrodes are formed first by laminating an electrothermal member of HfB.sub.2 as a heat generating resistive layer and metal layers of Al, Ti or the like as electrode layers on a substrate of glass, silicon, ceramic or the like, in order, by the use of sputtering or the like. This lamination is then formed with a preselected pattern by a photolithographic process utilizing a photoresist material (photosensitive resin). Finally, each layer is etched by the wet- or dry-etching process.
This etching process presents a certain problem needing to be improved and the improvement will be described below.
FIG. 1 is a fragmentary plan view showing, in an enlarged scale, an electro-thermal converting assembly formed in accordance with the prior art etching process. This assembly includes a substrate 101, a plurality of electrodes 102 and 103 formed on the substrate 101 and a heat generating portion 104 formed between each pair of electrodes 102, 103. As shown in FIG. 1, the assembly often has bridges 105 between each adjacent electrodes and bridges 106 between each adjacent heat generating resistive layers 107 (which layers are formed under the electrodes 102, 103 except the heat generating portion in the same pattern as that of the electrodes). These bridges 105 or 106 are formed of the electrode or heat generating resistive material which has remained on the substrate without being subjected to etching for any reason, which may, for example be due to residue on the substrate, a defect in the photomask, air bubbles produced on etching, or the like. The bridges highly decrease the reliability and production yield of the recording heads. The creation of the bridges 105 and 106 will further be increased as the density of the recording pattern is increased to improve the density of a recording head with a high-density multi-orifice, that is, when the spacings between each adjacent electrodes and between each adjacent heat generating resistive layers become smaller.
The bridges 105 and 106 can be removed, for example, by forming the same photoresist patterns on the substrate having these bridges and treating this pattern by etching so that the bridges will be dissolved and removed. This is however disadvantageous in that the end and side edges of the electrodes 102 and 103 are further etched into irregular edges as shown in FIG. 2(a) or the heat generating resistive layers 107 under the respective electrodes 102 and 103 are subjected to excessive etching as shown in FIG. 2(b). This means that the accuracy of finishing, the durability of the head portion contacting the liquid and the production yield will be decreased. Another method of removing the bridges may be provided by applying a high voltage to the electrodes 102 and 103 to burn away the bridges 106 with an excessive current. If the bridge 106 fails to be completely burnt away, however, its remainder provides irregular shapes or processes on the substrate 101. If the electrodes and heat generating portions are further covered by a protective layer, the latter also may more frequently be formed with defects. This, when the bridge remainder is on a head portion to be contacted by the ink, the latter may penetrate into the electro-thermal converting assembly to damage its electrodes 102, 103 and heat generating resistive layers 107. But even if the protective layer is not affected, or if no protective layer is used since the electrode and heat generating resistive layers are made of a material that has superior resistance to ink and mechanical strength, the current used to burn away the bridges will flow through the heat generating resistive layers and can damage them. Therefore, this method cannot also be used to remove the bridges since it decreases the reliability in produced recording heads.